Micrel Qwikradio micrf102 Owner's manual

September 2002 1 MICRF102

MICRF102 Micrel

MICRF102

QwikRadio™ UHF ASK Transmitter

Final Information

General Description

The MICRF102 is a single chip Transmitter IC for remote

wireless applications. The device employs Micrel’s latest

QwikRadio™ technology. This device is a true “data-in,

antenna-out”monolithicdevice. Allantennatuningisaccom-

plished automatically within the IC which eliminates manual

tuning, and reduces production costs. The result is a highly

reliable yet extremely low cost solution for high volume

wireless applications. Because the MICRF102 is a true

single-chip radio transmitter, it is easy to apply, minimizing

design and production costs, and improving time to market.

TheMICRF102usesanovelarchitecturewheretheexternal

loop antenna is tuned to the internal UHF synthesizer. This

transmitteris designedtocomplyworldwideUHFunlicensed

band intentional radiator regulations. The IC is compatible

with virtually all ASK/OOK (Amplitude Shift Keying/On-Off

Keyed)UHFreceiver typesfromwide-bandsuper-regenera-

tive radios to narrow-band, high performance super-hetero-

dyne receivers. The transmitter is designed to work with

transmitter data rates from 100 to 20k bits per second.

Theautomatictuninginconjunctionwiththeexternalresistor,

insures that the transmitter output power stays constant for

the life of the battery.

WhencoupledwithMicrel’sfamilyofQwikRadio™receivers,

the MICRF102 provides the lowest cost and most reliable

remote actuator and RF link system available.

Typical Application

VDD

VSS

REFOSC

ASK

MICRF102

ASK DATA INPUT

RP2

6.8k

0.1µF

4.7µF

RP1

100k

+5V

ANTP

ANTM

STBY

LOOP

ANTENNA

(PCB TRACE)

100k

Figure 1

Features

•Complete UHF transmitter on a monolithic chip

•Frequency range 300MHz to 470MHz

•Data rates to 20kbps

•Automatic antenna alignment, no manual adjustment

•Low external part count

•Low standby current <0.04µA

Applications

•Remote Keyless Entry Systems (RKE)

•Remote Fan/Light Control

•Garage Door Opener Transmitters

•Remote Sensor Data Links

Ordering Information

Part Number Temperature Range Package

MICRF102BM –0°C to +85°C 8-Pin SOIC

Micrel, Inc. •1849 Fortune Drive •San Jose, CA 95131 •USA •tel + 1 (408) 944-0800 •fax + 1 (408) 944-0970 •http://www.micrel.com

QwikRadio is a trademark of Micrel, Inc. The QwikRadio ICs were developed under a partnership agreement with AIT of Orlando, Florida

MICRF102 Micrel

MICRF102 2 September 2002

Pin Description

Pin Number Pin Name Pin Function

1 PC Power Control Input. The voltage at this pin should be set between 0.15V to

0.35V for normal operation.

2 VDD Positive power supply input for the IC.

3 VSS This pin is the ground return for the IC. A power supply bypass capacitor

connected from VDD to VSS should have the shortest possible path.

4 REFOSC This is the timing reference frequency which is the transmit frequency

divided by 32. Connect a crystal (mode dependent) between this pin and

VSS, or drive the input with an AC coupled 0.5Vpp input clock. See

Refer-

ence Oscillator

Section in this data sheet

5 STBY Input for transmitter stand by control pin is pulled to VDD for transmit

operation and VSS for stand-by mode.

6 ANTM Negative RF power output to drive the low side of the transmit loop antenna

7 ANTP Positive RF power output to drive the high side of the transmit loop antenna

8 ASK Amplitude Shift Key modulation data input pin. For CW operation, connect

this pin to VDD

Pin Configuration

1PC

VDD

VSS

REFOSC

8 ASK

ANTP

ANTM

STBY

MICRF102BM

September 2002 3 MICRF102

MICRF102 Micrel

Electrical Characteristics

Specifications apply for 4.75V < VDD < 5.5V, VPC = 0.35V, TA= 25°C, freqREFOSC = 12.1875MHz, STBY = VDD. Bold values indicate

0°C ≤TA ≤85°C unless otherwise noted.

Parameter Condition Min Typ Max Units

Power Supply

Standby Supply Current, IQVSTBY < 0.5V, VASK < 0.5V or VASK > VDD –0.5V 0.04 µA

MARK Supply Current, ION @315MHz, Note 4 610.5 mA

@433MHz, Note 4 812 mA

SPACE Supply Current, IOFF @315MHz 4 6mA

@433MHz 6 8.5 mA

Mean Operating Current 33% mark/space ratio at 315MHz, Note 4 4.7 mA

33% mark/space ratio at 433MHz, Note 4 6.7 mA

RF Output Section and Modulation Limits:

Output Power Level, POUT @315MHz; Note 4, Note 5 tbd dBm

@433MHz; Note 4, Note 5 tbd dBm

Transmitted Power @315MHz tbd µV/m

@433MHz tbd µV/m

Harmonics Output, Note 10 @ 315MHz 2nd harm. –46 dBc

3rd harm. –45

@433 MHz 2nd harm. –50 dBc

3rd harm. –41

Extinction Ratio for ASK 40 52 dBc

Varactor Tuning Range Note 7 3 57pF

Reference Oscillator Section

Reference Oscillator Input 300 kΩ

Impedance

Reference Oscillator Source 6µA

Current

Reference Oscillator Input 0.2 0.5 VPP

Voltage (peak to peak)

Absolute Maximum Ratings (Note 1)

Supply Voltage(VDD) .....................................................+6V

Voltage on I/O Pins ............................. VSS–0.3 to VDD+0.3

Storage Temperature Range ..................–65°C to + 150°C

Lead Temperature (soldering, 10 seconds) ...........+ 300°C

ESD Rating .............................................................. Note 3

Operating Ratings (Note 2)

Supply Voltage (VDD) .................................... 4.75V to 5.5V

Maximum Supply Ripple Voltage ...............................10mV

PC Input Range..............................150mV < VPC < 350mV

Ambient Operating Temperature (TA) ............0°C to +85°C

Programmable Transmitter Frequency Range:

.................................................... 300MHz to 470MHz

MICRF102 Micrel

MICRF102 4 September 2002

Parameter Condition Min Typ Max Unit

Digital / Control Section

Calibration Time Note 8, ASK=HIGH 25 ms

Power Amplifier Output Hold Off Note 9, STDBY transition from LOW to HIGH 6 ms

Time from STBY Crystal, ESR < 20Ω

Transmitter Stabilization Time From External Reference (500mVpp) 10 ms

from STBY Crystal, ESR < 20Ω19 ms

Maximum Data Rate

–ASK modulation Duty cycle of the modulating signal = 50% 20 kbits/s

VSTBY Enable voltage 0.75VDD 0.6VDD V

STBY Sink Current ISTBY = VDD 56.5 µA

ASK pin VIH, input high voltage 0.75VDD 0.6VDD V

VIL, input low voltage 0.3VDD 0.25VDD V

ASK input current ASK = 0V, 5.0V input current –10 0.1 10 µA

Note 1. Exceeding the absolute maximum rating may damage the device.

Note 2. The device is not guaranteed to function outside its operating rating.

Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.

Note 4. Supply current and output power are a function of the voltage input on the PC (power control) pin. All specifications in the Electrical Charac-

teristics table applies for condition VPC = 350mV. Increasing the voltage on the PC pin will increase transmit power and also increase MARK

supply current. Refer to the graphs "Output Power Versus PC Pin Voltage" and "Mark Current Versus PC Pin Voltage."

Note 5. Output power specified into a 50Ωequivalent load using the test circuit in Figure 5.

Note 6. Transmitted power measured 3 meters from the antenna using transmitter board TX102-2A in Figure 6.

Note 7. The Varactor capacitance tuning range indicates the allowable external antenna component variation to maintain tune over normal production

tolerances of external components. Guaranteed by design not tested in production.

Note 8. When the device is first powered up or it loses power momentarily, it goes into the calibration mode to tune up the transmit antenna.

Note 9. After the release of the STDBY, the device requires an initialization time to settle the REFOSC and the internal PLL. The first MARK state

(ASK HIGH) after exit from STDBY needs to be longer than the initialization time. The subsequent low to high transitions will be treated as

data modulation whereby the envelope transition time will apply.

Note 10. The MICRF102 was tested to be Compliant to Part 15.231 for maximum allowable TX power, when operated in accordance with a loop

antenna described in Figure 6.

September 2002 5 MICRF102

MICRF102 Micrel

Typical Characteristics

0 100 200 300 400 500 600

CURRENT (mA)

(mV)

Mark Current vs

PC Pin Volta

-35

-30

-25

-20

-15

-10

-5

0 100 200 300 400 500 600

OUTPUT POWER (dBm)

VPC (mV)

Output Power vs

PC Pin Volta

MICRF102 Micrel

MICRF102 6 September 2002

Functional Description

The block diagram illustrates the basic structure of the

MICRF102. Identifiedinthefigurearetheprincipalfunctional

blocks of the IC, namely the (1, 2, 3, 4, 5) UHF Synthesizer,

(6a/b) Buffer, (7) Antenna tuner, (8) Power amplifier, (9) TX

bias control, (10) Reference bias and (11) Process tuner.

The UHF synthesizer generates the carrier frequency with

quadrature outputs. The in-phase signal (I) is used to drive

the PA and the quadrature signal (Q) is used to compare the

antenna signal phase for antenna tuning purpose.

The Antenna tuner block senses the phase of the transmit

signalat theantennaportandcontrolsthevaractor capacitor

to tune the antenna.

The Power control unit senses the antenna signal and con-

trolsthePA bias current toregulate the antennasignal to the

transmit power.

Functional Diagram

Bias

Control

Varactor

Device

Antenna

Tuning

Control

Power

Amp

Buffer

VSS

ANTM

ANTP

ASK

Buffer

Prescaler

Divide

by 32

REF.OSC

VDD

VDD (10)

(5)

(2)

Reference

Oscillator (1)

VCO (4)

(3)

(9) (8)

(7)

(11)

(6a)

(6b)

STBY Reference

Bias

Phase

Detector

Figure 2. MICRF102 Block Diagram

The Process tune circuit generates process independent

bias currents for different blocks.

A PCB antenna loop coupled with a resonator and a resistor

divider network are all the components required to construct

acompleteUHFtransmitterforremoteactuationapplications

such as automotive keyless entry.

Included within the IC is a differential varactor that serves as

the tuning element to insure that the transmit frequency and

antenna are aligned with the receiver over all supply and

temperature variations.

September 2002 7 MICRF102

MICRF102 Micrel

Applications Information

Design Process

The MICRF102 transmitter design process is as follows:

1). Set the transmit frequency by providing the

correct reference oscillator frequency

2). Ensure antenna resonance at the transmit

frequency by:

LANT = 0.2 ×Length ×ln(Length/d - 1.6) ×10-9 ×k

Where:

Length is the total antenna length in mm.

d is the trace width in mm.

k is a frequency correction factor.

LANT is the approximate antenna inductance in

henries.

Note 1. The total inductance however will be a little greater

than the LANT calculated due to parasitics. A 2nH should be

added to the calculated value. The LANT formula is an

approximatedwaytocalculatetheinductanceoftheantenna.

The inductance value will vary however, depending on pcb

material,thickness,groundplane,etc.Themostpreciseway

to measure is to use a RF network analyzer.

3). Calculate the total capacitance using the follow-

ing equation.

CfL

TANT

=×××

()

422

ππ

Where:

CTtotal capacitance in farads.

π= 3.1416.

f = carrier frequency in hertz.

LANT inductance of the antenna in henries.

4). Calculate the parallel and series capacitors,

which will resonate the antenna.

4.1). Ideally for the MICRF102 the series and parallel

capacitors should have the same value or as

close as possible.

4.2). Start with a parallel capacitor value and plug in

the following equation.

CC C

T VAR P

=−+

()











Where:

CVAR is the center varactor capacitance (5pF for the

MICRF102) in farads.

CPis the parallel capacitor in farads.

CSis the series capacitor in farads.

Repeat this calculation until CSand CPare very close and

they can be found as regular 5% commercial values.

Note2.Ideally,theantennasizeshouldnotbelargerthanthe

oneshownhere. Thebiggertheantennaarea, thehigherthe

loaded Q in the antenna circuit will be. This will make more

difficult to match the parallel and series capacitors. Another

point to take into consideration is the total ac rms current

going through the internal varactor in the MICRF102. This

current should not exceed 16mA rms. The parallel capacitor

will absorb part of this current if the antenna dimensions are

appropriate and not exaggerated larger than the one shown

here.

Note 3. A strong indication that the right capacitor values

havebeenselected is the meancurrent with a1kHz signal in

the ASK pin. Refer to the

Electrical Characteristics

for the

current values.

Note4.Formuch smaller antennas, placeablockingcapaci-

tor for the series capacitance (around 100pF to 220pF) and

usethefollowingformulafortheparallelcapacitanceCT=CP

+ CVAR. The blocking capacitor is needed to ensure that no

dc current flows from one antenna pin to the other.

5.) Set PC pin to the desired transmit power.

Reference Oscillator Selection

Anexternalreferenceoscillatorisrequiredtosetthetransmit

frequency. The transmit frequency will be 32 times the

reference oscillator frequency.

TX REFOSC

=×32

Crystalsorasignalgeneratorcanbeused.Correctreference

oscillator selection is critical to ensure operation. Crystals

must be selected with an ESR of 20 Ohms or less. If a signal

generator is used, the input amplitude must be greater than

200 mVP-P and less than 500 mVP-P.

Antenna Considerations

The MICRF102 is designed specifically to drive a loop an-

tenna. It has a differential output designed to drive an induc-

tive load. The output stage of the MICRF102 includes a

varactor that is automatically tuned to the inductance of the

antenna to ensure resonance at the transmit frequency.

A high-Q loop antenna should be accurately designed to set

the center frequency of the resonant circuit at the desired

transmitfrequency.Anydeviationfromthedesiredfrequency

will reduce the transmitted power. The loop itself is an

inductive element. The inductance of a typical PCB-trace

antennaisdeterminedbythesizeoftheloop,thewidthofthe

antenna traces, PCB thickness and location of the ground

plane.Thetoleranceoftheinductanceissetbythemanufac-

turing tolerances and will vary depending how the PCB is

manufactured.

The MICRF102 features automatic tuning. The MICRF102

automaticallytunesitselftotheantenna,eradicatingtheneed

formanualtuningin production. Italsodynamicallyadaptsto

changesinimpedance inoperationandcompensates forthe

hand-effect.

Automatic Antenna Tuning

The output stage of the MICRF102 consists of a variable

capacitor (varactor) with a nominal value of 5.0pF tunable

over a range from 3pF to 7pF. The MICRF102 monitors the

phase of the signal on the output of the power amplifier and

automaticallytunestheresonantcircuitbysettingthevaractor

value at the correct capacitance to achieve resonance.

MICRF102 Micrel

MICRF102 8 September 2002

In the simplest implementation, the inductance of the loop

antenna should be chosen such that the nominal value is

resonantat5pF,thenominalmid-rangevalueoftheMICRF102

output stage varactor.

Using the equation:

LfC

ππ

Ifthe inductanceoftheantennacannot besetatthenominal

value determined by the above equation, a capacitor can be

added in parallel or series with the antenna. In this case, the

varactor internal to the MICRF102 acts to trim the total

capacitance value.

ANTENNA

VARACTOR

Figure 4.

Supply Bypassing

Correct supply bypassing is essential. A 4.7uF capacitor in

parallel with a 100pF capacitor is recommended.

The MICRF102 is susceptible to supply-line ripple, if supply

regulation is poor or bypassing is inadequate, spurs will be

evident in the transmit spectrum.

VDD

VSS

REFOSC

ASK

MICRF102

ASK DATA INPUT Transformer Output to 50‰

Impedance Transformation

Network

OFF

RP2

(6.8k)

RP1

(100k)

+5V

Crystal

Z1 Z3

ANTP

ANTM

STBY

To 50‰

Termination of

Spectrum Analyzer

Figure 5. Application Test Circuit For Specification Verification

Transmit Power

The transmit power specified in this datasheet is normalized

to a 50Ohm load. The antenna efficiency will determine the

actual radiated power. Good antenna design will yield trans-

mitpowerintherangeof67dBµV/mto80dBµV/mat3meters.

The PC pin on the MICRF102 is used to set the transmit

power.ThedifferentialvoltageontheoutputofthePA(power

amplifier) is proportional to the voltage at the PC pin.

With more than 0.35V on the PC pin the output amplifier

becomes current limited. At this point, further increase in the

PC pin voltage will not increase the RF output power in the

antenna pins. Low power consumption is achieved by de-

creasing the voltage in the PC pin, also reducing the RF

output power and maximum range.

Output Blanking

Whenthedeviceisfirstpowereduporafteramomentaryloss

of power the output is automatically blanked (disabled). This

feature ensures RF transmission only occurs under con-

trolled conditions when the synthesizer is fully operational,

preventing unintentional transmission at an undesired fre-

quency. Output blanking is key to guaranteeing compliance

withUHFregulationsbyensuringtransmissiononlyoccursin

the intended frequency band.

September 2002 9 MICRF102

MICRF102 Micrel

Design Examples

Complete reference designs including gerber files can be

downloaded from Micrel’s website at www.micrel.com/prod-

uct-info/qwikradio.shtml.

Antenna Characteristics

In this design, the desired loop inductance value is deter-

mined according to the table below.

Freq. R XL Ind Q K

(MHz) (ohms) (ohms) (nH) (XL/R)

300 1.7 84.5 44.8 39.72 0.83

315 2.34 89.3 45.1 39.65 0.85

390 3.2 161 47.4 52.00 0.90

434 2.1 136 50.0 78.33 0.96

The reference design shown in Figure 6. has an antenna

meeting this requirement.

Figure 6

Loopantennasareoftenconsideredhighlydirectional.Infact

small loop antennas can achieve transmit patterns close in

performance to a Dipole antenna. The radiation pattern

below is the theoretical radiation pattern for the antenna

shown in Figure 6.

E-total, phi = 0¡

E-total, phi = 90¡

(180-phi) direction phi direction

30.0

180.0

60.0

120.0

150.0

120.0

60.0

30.0 0.0

Figure 7. Polar Elevation pattern at 315MHz

The 0 degree plot is the radiation pattern in the plane of the

transmitter PCB, the 90 degree plot represents the plane

perpendicular to the PCB. Micrel’s evaluation of the perfor-

mance of the board in Figure 6. indicates an even more

uniformradiationpatternthatthetheoreticalplotshownhere.

Supply Bypassing

Supply bypassing consists of three capacitors; C3 = 4.7uF,

C4 = 0.1uFand C5 = 100pF

0.1 F

16V

100pF

50V

4.7 F

16V

+5VTX

VDD

MICRF102BM

PC1ASK 8

ANTP 7

ANTM 6

SB 5REFOSC4

Figure 8.

Example to Calculate CS and CP

Antenna Inductance Calculation

Length_mils = 2815

dmils = 70

k = 0.85

Length Length_mils 25.4

1000

Length 71.501

=×

()

ddmils

=×

()

25 4

1000

1 778

L 0.2 Length ln Length

d1.6 10 k

L4410

=× × −









××

=×

−

Where Length and d are in mm and L is in H;

Where k is a constant dependent on pcb material, copper

thickness, etc

MICRF102 Series Capacitor Calculation

f = 315 ×106

L = 46 ×10-9

CVAR = 5 ×10-12

CP= 12 ×10-12

ClfL

=×××

=×

−

555 10

ππ

SERIES

T VAR

SERIES

=−

=×

−

82 1012

MICRF102 Micrel

MICRF102 10 September 2002

MICRF102 Series Capacitor Calculation

f = 433.92 ×106

L = 52 ×10-9

CVAR = 5 ×10-12

CP= 2.7 ×10-12

CfL

=×××

=×

−

2 587 10

ππ

CC C

SERIES

T VAR P

SERIES

=−+

=×

−

39 1012

L1 = 52 ×10-9

f1 = 433.92 ¥106

CfL

122

112

2 587 10

=×××

=×

−

ππ

September 2002 11 MICRF102

MICRF102 Micrel

Package Information

45°3°–6°

0.244 (6.20)

0.228 (5.80)

0.197 (5.0)

0.189 (4.8)

0.063 (1.60) MAX

SEATING

PLANE

0.026 (0.65)

MAX)

0.016 (0.40)

TYP

0.154 (3.90)

0.057 (1.45)

0.049 (1.25)

0.193 (4.90)

0.050 (1.27)

TYP

PIN 1

DIMENSIONS:

INCHES (MM)

8-Pin SOP (M)

MICRF102 Micrel

MICRF102 12 September 2002

MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com

This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or

other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel, Inc.

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